August 2016

By 2016, I had my own collection of breadboards and TTL components, and was ready to move ahead and make this breadboard computer "compute". We had dropped the 74LS244s and 74LS374s, but had added 74LS574s. The 574 acts as an 8-bit register that has inputs and outputs lined up to make bread-boarding really easy. We also added the first part of an ALU, creating 8-bit adders using 74LS183s. I forget if my friend got his working, but we ended the session before I could get my adder working 100% of the time.

We each worked on our own version of the computer, but with the plan that they would be similar enough to share basic programs when completed. By the end of the two days, we both had a lot working... although all of it was controlled by the RaspberryPi.

• RPi interface, reading from and writing to an 8-bit data bus,
• XL and XH address registers, with multiplexor,
• Working 32k of SRAM, addressed via the XL and XH registers,
• 8-bit Adder, with 72LS244 buffer to control output to the data bus (buggy)